The proposed project is to study factors controlling the proliferation and maturation of granulocytes in vivo and in vitro. The major emphasis is directed toward the study of in vitro proliferation of colonies of granulocytic and mononuclear cells from marrow and blood of animals and man. Colonies are cultured in a soft gel system (agar or methylcellulose) in the presence of a colony stimulating activity (CSA). Human and animal cells will also be cultured in liquid suspension. Studies will include the following: 1) to determine the role of complement on granulocyte production and kinetics, 2) to identify the population of spleen lymphocytes which suppress granulopoiesis in vitro, 3) to characterize properties of a human acute leukemia cell line growing in suspension culture, 4) to determine the mechanism of leukopenia in viral diseases, 5) to determine factors regulating the mechanisms of lithium induced granulocytosis.